1. Field of the Invention
The present invention relates generally to a multi-ratio transmission system, more particularly, relates to a multi-ratio transmission system with parallel vertical and coaxial planet gears which can be used on bicycles, transportation vehicles or other devices.
2. The Prior Arts
Mechanical multi-ratio transmission systems are widely used in many different kinds of power machineries and equipments. The main purpose of the mechanical multi-ratio transmission system is to provide the change in rotation speeds and torques between the input end and the output end of the machinery.
The bicycle derailleur is one of the commonly seen multi-ratio transmission systems, which is mainly composed of different sizes of sprockets. As shown in FIG. 1, the bicycle derailleur system 900 includes multiple sprockets 902 which are coaxially disposed on the bicycle along bicycle wheel axle 904, e.g. the rear bicycle wheel axis. The sprockets 902 are connected to the bicycle pedals through a chain 906. In the system described above, derailing the chain 906 between sprockets 902 of different sizes can change the rotation speed ratio between the rear bicycle wheel and the pedal. Due to the nature of the structure of the derailleur, the axial size of the derailleur system would increase as more sprockets are added to the system. Therefore, only a limited number of sprockets can be used in such derailleur system to prevent the size of the system from becoming too large and thus interfering with the operation of the machinery or equipment. However, since each sprocket represents a different rotation speed, the number of the sprockets determines the number of transmission ratios available in a bicycle derailleur system. Hence, under the condition that the number of sprockets is limited, the number of the transmission ratios that can be provided by the derailleur is also limited.
Another type of commonly seen multi-ratio transmission system is the gear shifting system of the mobile vehicles, such as the ones in the automobiles or motorcycles. As shown in FIG. 2, such gear shifting system 920 usually have multiple sets of gears 924 that are engaged to one another installed within a metal casing 922. These gears 924 rotate around axles that are separately disposed from one another, and optionally slide on the axles to achieve different engagement status of the gears 924, thereby achieving the change in the speed ratio and torque between the output end and the input end. The gears 924 and the axles of the gears have the same size. In order to provide enough space for the gears to move around, the size of such gear shifting system is relatively large. In addition, similar to the derailleur of the bicycle, the number of the transmission ratios that can be achieved is also determined by the number of the gears in the system; therefore, when the number of gears is limited due to the limitation of the actual design of such system, the number of the transmission ratios that can be provided is also limited.
On the other hand, planet gear system is an effective way to reduce the size of the gear transmission system in the mechanical industry. FIG. 3 is an example of a commonly seen planet gear system. As shown in FIG. 3, the planet gear system 940 includes a sun gear 942 and an annular gear 944. The sun gear 942 and the annular gear 944 are coaxially placed with each other to form an annular space within. Multiple planet gears 946 are placed inside the annular space to simultaneously engage with the sun gear 942 and the annular gear 944. With such configuration, the sun gear 942, the annular gear 944 and the planet gears 946 basically rotate in different speed. When the planet gear system as described above is in use, each of the sun gear, the planet gear and the annular gear serve as the input end or the output end to change the rotation speed and the torque between the input end and the output end. However, the number of transmission ratio that can be achieved by a single planet gear system is limited; hence, two sets or more of the planet gear systems are often coupled together in the axial direction to increase the number of the transmission ratio or torque available. In addition, the rotation axes of the planet gears are parallel to the rotation axis of the sun gear, which still result in the increase of the overall size of the system.
Furthermore, similar to the derailleur of the bicycle and the gear shifting system of the automobile or motorcycle, axially coupling multiple planet gear systems together still increases the overall size of the multi-ratio transmission system, which is a disadvantage to the application of the system.
Therefore, it is urgently needed for the industry to develop a type of the multi-ratio transmission system that can provide a large number of transmission ratios while maintaining an overall small size of the system.